Actuatable drivescrew device

ABSTRACT

A drivescrew is provided with a sleeve-type housing containing a plurality of balls engageably associated with that portion of the helical threads of the screw translatably disposed therewithin, the balls being actuatably prevented or permitted to revolve with the threads of the screw to thereby translate or not translate, respectively, the sleeve-type housing along the screw as the latter is rotated.

I Umte States i atent n 1 3,636,780 Wallace Jan. 25, 1972 1 ACTUATABLEDRIVESCREW DEVICE 2,824,460 2/1958 Davis ..74/DlG. 4 Inventor: m L.Wallace, Garden C y Mich. 3,258,983 7/1966 Valenti ,..74/459 [73]Assignee: Burroughs Corporation, Detroit, Mich. Primary ExaminerwilliamODea Assistant ExaminerWesley S. Ratliff, Jr. [22] Fled: 1970Att0rneyl(enneth L. Miller and Edwin W. Uren [21] A 1. No.: 17 86 pp ,3[57] ABSTRACT 52 us. Cl. ..74 s9.1s, 74/424.8 NA 74/459 A drivescrew isPmvided with a Sleeve-type musing 7:4/DIG ing a plurality of ballsengageably associated with that portion 51 Int. c: ..Fl6h 27/02 thehelical the screw disposed [58] Field of Search 74/895, 459 DIG 4, 424 8NA therewithin, the balls being actuatably prevented or permitted torevolve with the threads of the screw to thereby translate or [56]References Cited not translate, respectively, the sleeve-type housingalong the screw as the latter is rotated.

UNITED STATES PATENTS 5 Clalms, 4 Drawing Figures 2,478,510 8/1949Stolpe ,.74/459 PATENTEDJANZSISZZ 3.636780 INVENTOR HARRY LWALLACE AGENTACTUATABLE DRIVESCREW DEVICE BACKGROUND OF THE INVENTION The inventionrelates to mechanisms transposing rotary to linear, axial movement usingassociated external and internal screws.

Prior art discloses drivescrew devices using rotating external screwsthreaded through rotationally stationary internal screws. A typicalexample may be found in a print carrier drive mechanism, where a printhead is mounted on a carrier to be driven longitudinally along a platen.Such carriers include an internally threaded member adapted to receivean externally threaded drivescrew which, when rotated, translates thecarrier axially along the platen. The threads of both the externallythreaded drivescrew and the internally threaded member are fixed and inconstant engagement, carrier movement being initiated and halted byrespectively rotating and stopping the externally threaded drivescrew.

Other typical print carrier drive mechanisms include similar internallyand externally threaded drive members to translate carriers and alsoinclude limited-slip friction devices to couple drive to the externallythreaded screws or to couple the internally threaded members to theirrespective carriers. In these latter mechanisms, drive is appliedcontinuously; and carrier translation is controlled by mechanical stops.

The mechanism described in the first example is subject to fatigue andwear due to the inherent necessity for frequently starting and stoppingthe drivescrew, thus increasing the cost of construction andmaintenance.

The limited-slip friction devices described in the second exampleprovide drive which is a function of ambient environmental conditionssuch as temperature and humidity and is therefore inconstant. As thefriction devices wear with use, the frictional coupling factor isaltered, normally declining, eventually resulting in a maintenanceproblem. The heat generated by the friction surfaces also contributes toalternating the coupling factor and, in extreme cases, may evendeleteriously affect adjacent components; and its dissipation presents aproblem which must be considered, frequently adding to the cost ofdesign and manufacturing. Since at least a minimal amount of drive iscontinuously applied to the carrier, relatively substantial stops arerequired, again adding to the cost of construction.

The threads of the mechanisms of both of the abovedescribed examples arenaturally subject to wear, which gives rise to yet another maintenanceproblem in the area of print location accuracy.

SUMMARY OF THE INVENTION The invention resides in the provision of anactuatable drivescrew device to produce translation of an internallythreaded member axially along an externally threaded screw.

Accordingly, it is an object of the present invention to provide anactuatable drivescrew device operable with continuously applied driveand wherein fatigue and wear resulting from component accelerations areminimized.

It is another object of the invention to provide a drive device which ispositive and constant and not subject to variations due to changes inambient environmental conditions.

It is yet another object of the invention to provide an actuatabledrivescrew device which is positively coupled, thus eliminating themaintenance and operational problems inherent in friction drive devices.

Still another object of the invention is to provide a drive device whichwill generate no appreciable heat at the point of drive coupling andthus eliminate the usual wear, drive variation and heat-dissipationproblems.

Another object of the invention is to provide a simple and reliabledrive device which will require relatively light and inexpensivemechanical stops to halt axial translations.

Yet another object of the invention is to provide a drivescrew devicewhich uses balls as the threads of one of the screw members, therebysubstantially reducing drive thread wear.

An important aspect of the invention is the use of balls as a means ofcoupling the drive of a rotating screw to a translating member, theballs performing the function of the internal threads of the translatingmember which mesh with the threads of the rotating driving screw member.

Another important aspect of the invention is means for selectivelypermitting the balls to revolve with the rotating screw and toindividually rotate in typical ball-bearing-effect fashion, or to holdthem fixed with respect to the translating member so as to function asintegral threads thereof and to thereby drive the translating memberaxially along the rotating screw.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, aspects andadvantages of the invention will be more clearly understood from thefollowing description when read in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a plan view of an actuatable drivescrew device embodyingfeatures of the invention,

FIG. 2 is a side view, partly in section, taken in the direction of thearrows 2-2 of FIG. 1,

FIG. 3 is a plan view of another embodiment of the invention, and

FIG. 4 is a side view, partly in section, taken in the direction of thearrows 4-4, of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, theactuatable drivescrew device shown has a rotatable external screw 10, aninternal screw 12, an internal screw housing 14 and an internal screwactuator 16. The internal screw 12 is disposed around the external screw10 by the internal screw housing. 14 in such a manner as to assume anengageable relationship with the threads of the external screw 10. Theinternal screw actuator 16 is effectively positioned proximate theinternal screw 12.

The external screw 10 is effectively a shaft having threads helicallycircumscribing its periphery. The internal screw 12 includes a pluralityof balls 18 mutually juxtaposed in a portion of the helical thread ofthe external screw 10, the balls 18 having freedom to individuallyrotate.

The internal screw housing 14 includes a circular sleeve 20 having aninternal diameter slightly larger than the outside diameter of theexternal screw 10. The sleeve 20 is positioned around that length of theexternal screw 10 whereon the balls 18 are located, thereby maintainingtheir effective relationship with the external screw l0. Also includedin the housing 14 are annular abutments 22 affixed to opposite ends ofthe sleeve 20 to receive the external screw 10 and to contain the balls18 within the sleeve.

With reference to FIGS. 1 and 2, a first embodiment of the invention isshown wherein the internal screw actuator 16 is a stop 24 insertablethrough the sleeve 20 to intercept one of the balls 18 in its path ofrevolution within the sleeve 20. This stop is resiliently biased awayfrom the balls 18 by a helical spring 26, which returns the stop to arest position when actuation of the device is terminated. FIG. 2 showsthe stop 24 in it actuated position.

With reference to FIGS. 3 and 4, a second embodiment of the invention isshown wherein the internal screw actuator I6 is an electromagnetic coil28 wound around the outer surface of the sleeve 20. In this embodiment,the external screw 10 is constructed of nonmagnetic material; and theballs I8 are ferromagnetic. The coil 28 is so wound that its magneticfield will effectively influence the balls 18 when it is energized.Covering the coil 28 is a shield 30 of nonconducting material, such'shield providing protective insulation to the coil.

OPERATION OF THE INVENTION With reference to FIGS. 1 and 2, theoperation of the first embodiment may be illustrated. The external screw10 may be rotated by any one of a number of common business machinemotors (not shown) in, for example, a counterclockwise direction asviewed from the left end thereof. The stop 24 is normally held in itsrest position away from the balls 18 by the spring 26. With the stop sopositioned, rotation of the external screw within the housing 14 willcause the balls 18 to revolve around the interior surface of the sleeve20. Since the balls are free to individually rotate as they so revolve,a ball bearing effect is provided between the external screw 10 and thesleeve 20, thereby permitting the internal screw housing 14 to remainmotionless despite the rotation of the external screw.

To actuate the device for translation of the housing 14, the stop 24 isurged to the position shown in FIG. 2 by any suitable apparatus (notshown) commonly used for such purposes. in this actuated position, thestop 24 is disposed in the path of revolution of the balls 18 andeffectively intercepts one of the balls, thereby stopping the revolutionof all of the balls both with respect to their individual rotation andtheir curvilinear revolution around the interior surface of the sleeve20. Since the threads of the external screw 10 are inclined to the left,as this rotating screw attempts to force the balls 18 to revolve, acomponent of the force exerted is directed to the right to thereby drivethe internal screw housing 14 in a corresponding direction.

When the housing 14, to which may be attached, for example, a print headcarrier, has been translated the distance desired, the stop 24 isreleased and returned by the spring 26 to its rest position away fromthe balls 18. Since the balls are now free to revolve within the sleeve20, the housing 14 is permitted to, idle in a fixed position on therotating external screw 10.

With reference to FIGS. 3 and 4, the operation of the second embodimentmay be illustrated. The external screw 10 is rotated as in the firstembodiment in, for example, a counterclockwise direction as viewed fromthe left end thereof. The balls 18 revolve around the interior surfaceof the sleeve as previously described, again acting as a ball bearingbetween the external screw 10 and the sleeve 20, permitting the internalscrew housing 14 to remain motionless while the external screw 10rotates.

To actuate the device, the coil 28 is electrically energized, thuscreating a magnefic field. Since the balls 18 are constructed of aferromagnetic material, they are so affected by the field that theirrevolving motion is stopped; and they are accordingly rendered fixed andstationary relative to the sleeve 20. As in the first embodiment, therotating external screw 10, in attempting to force the balls 18 torevolve, drives the internal screw housing 14 to the right in responseto the component of force acting in a corresponding direction as aconsequence of the combined effect of the direction of rotation of theexternal screw and the left-inclined threads thereof.

When the desired translation has been completed, the electromagneticcoil 28 is deenergized, collapsing its magnetic filed. The balls 18 areaccordingly released from their fixed and stationary state and arepermitted once again to revolve around the interior surface of thesleeve 20 and to thereby cause the interior screw housing 14 to idle ina fixed position.

Although, for the purpose of explanation, the method for translating theinternal screw housing 14 to the right was detailed, it should beevident that the procedure would suffice equally for translating it tothe left, were the external screw 10 merely rotated in the oppositedirection, that is, in a clockwise direction as viewed from the left endthereof. Indeed, reversing the direction of rotation of the externalscrew 10 would serve as a perfectly adequate method for returning theinternal screw housing 14 to a rest or home position after its desiredtranslation has been completed. Another functional means for returningthe internal screw housing 14 to a home position would be the provisionof a resilient member (not shown) operatively connected between thehousing and the supporting means and displaceable by the housingtranslations such that, when the drivescrew device is not actuated andnot held at an advanced position the resilient member would force thehousing back along the external screw 10, the balls 18 being at thistime free both to individually rotate and to revolve within the housing.

While the actuatable drivescrew device has been shown and described inconsiderable detail, it should be understood that many changes andvariations may be made therein without departing from the spirit andscope of the invention.

I claim:

1. An actuatable drivescrew device comprising:

a rotatable external screw having helical threads;

an actuatable internal screw formed of a plurality of individuallyrotatable balls and effectively engageable with said external screw;

an internal screw housing for effectively enclosing said balls aroundsaid screw, said housing having an internally smooth, cylindrical sleevefor maintaining said balls in a helically adjacent relationship definedby the threads of said external screw and also having an annularabutment disposed at each end of said sleeve for preventing said ballsfrom escaping their helically ordered confine within said sleeve, saidinternal screw normally being free to rotate with said external screwwithin said housing; and

an internal screw-actuating member for selectively actuating saidinternal screw, said actuating member being a stop selectivelypositionable in the path of revolution of at least one of said balls,thereby preventing said internal screw from rotating with said externalscrew within said housing, said balls collectively forming internalthreads fixed with respect to said housing and effectively engaging thethreads of said external screw such that rotation of said latter screwproduces longitudinal translation of said housing relative thereto.

2. The actuatable drivescrew device defined by claim 1 wherein said stopis insertable through said sleeve.

3. The actuatable drivescrew device defined by claim 1 wherein said stopis resiliently biased out of the paths of revolution of said balls.

4. The actuatable drivescrew device defined by claim 1 wherein saidexternal screw is a helically threaded shaft.

5. A method for selectively transposing rotary to linear motioncomprising the steps of: inserting a rotatable, external screwlongitudinally through an internally smooth, sleeve-type housingcontaining a plurality of individually rotatable balls therein such thatsaid balls are disposed in a helically adjacent relationship along thosethreads of said external screw that are within said housing; rotatingsaid external screw within said housing, said balls normally beingrevolvable with said external screw along the smooth, internal surfaceof said housing; and inserting a selectively insertable stop into thepath of revolution of at least one of said balls, thereby preventing allof said balls from revolving with said external screw, said ballsforming internal threads stationary with respect to said housing andeffectively engaging the threads of said external screw such thatrotation of said latter screw produces longitudinal translation of saidhousing relative thereto.

1. An actuatable drivescrew device comprising: a rotatable externalscrew having helical threads; an actuatable internal screw formed of aplurality of individually rotatable balls and effectively engageablewith said external screw; an internal screw housing for effectivelyenclosing said balls around said screw, said housing having aninternally smooth, cylindrical sleeve for maintaining said balls in ahelically adjacent relationship defined by the threads of said externalscrew and also having an annular abutment disposed at each end of saidsleeve for preventing said balls from escaping their helically orderedconfine within said sleeve, said internal screw normally being free torotate with said external screw within said housing; and an internalscrew-actuating member for selectively actuating said internal screw,said actuating member being a stop selectively positionable in the pathof revolution of at least one of said balls, thereby preventing saidinternal screw from rotating with said external screw within saidhousing, said balls collectively forming internal threads fixed withrespect to said housing and effectively engaging the threads of saidexternal screw such that rotation of said latter screw produceslongitudinal translation of said housing relative thereto.
 2. Theactuatable drivescrew device defined by claim 1 wherein said stop isinsertable through said sleeve.
 3. The actuatable drivescrew devicedefined by claim 1 wherein said stop is resiliently biased out of thepaths of revolution of said balls.
 4. The actuatable drivescrew devicedefined by claim 1 wherein said external screw is a helically threadedshaft.
 5. A method for selectively transposing rotary to linear motioncomprising the steps of: inserting a rotatable, external screwlongitudinally through an internally smooth, sleeve-type housingcontaining a plurality of individually rotatable balls therein such thatsaid balls are disposed in a helically adjacent relationship along thosethreads of said external screw that are within said housing; rotatingsaid external screw within said housing, said balls normally beingrevolvable with said external screw along the smooth, internal surfaceof said housing; and inserting a selectively insertable stop into thepath of revolution of at least one of said balls, thereby preventing allof said balls from revolving with said external screw, said ballsforming internal threads stationary with respect to said housing andeffectively engaging the threads of said external screw such thatrotation of said latter screw produces loNgitudinal translation of saidhousing relative thereto.